Linux Systemd

Basics

sudo systemctl daemon-reload
sudo systemctl enable some.service
sudo systemctl start some.service
sudo systemctl is-active some.service
sudo systemctl restart some.service
sudo systemctl stop some.service
sudo systemctl cat some.service
sudo systemctl disable some.service

Remove service

Stop and Disable service.

rm /etc/systemd/system/SERVICE_NAME
rm /usr/lib/systemd/system/SERVICE_NAME
systemctl daemon-reload
systemctl reset-failed

journalctl - show log of service

TAIL LOG

journalctl -f -u SERVICE_NAME.service

Show all log messages

journalctl -u SERVICE_NAME.service

Just since boot

journalctl -b -u SERVICE_NAME.service

cat like style

journalctl -b --no-pager -u SERVICE_NAME.service

Show log from the END

journalctl -b -e -u SERVICE_NAME.service

cat RAW log (same way as process)

journalctl -f -b -u SERVICE_NAME.service -o cat

journald maintenance

Maintenance of /var/log/journal/4c74c042939f4af8971cc0decb93d3d8/... for example.

journalctl --disk-usage
journalctl --vacuum-size=500M

Set desired values in /etc/systemd/journald.conf

SystemMaxUse=1024M
MaxRetentionSec=1month

And restart daemon systemctl restart systemd-journald.service. More info on SO

Edit existing unit

systemctl edit --full systemd-networkd-wait-online.service

Add TimeoutStartSec=5 in [Service] section, if Ubuntu start taking forever ...

BASH script to unit - AltServer example

altserver.service

[Unit]
Description=Alt Server
Wants=network-online.target
After=network-online.target

[Service]
User=root
Group=root
Type=simple
TimeoutStartSec=30
Restart=on-failure
RestartSec=30s
WorkingDirectory=/root
ExecStart=/root/runAltLinux.sh
SyslogIdentifier=AltServer

[Install]
WantedBy=multi-user.target

runAltLinux.sh

#!/bin/bash

while true
do
    RUN_DATE=$(date +"%Y%m%d_%H%M%S")
    RUN_SESSION="alt_${RUN_DATE}"
    tmux new-session -d -s "${RUN_SESSION}"
    tmux send-keys -t "${RUN_SESSION}:0" "while true ; do python3 main.py ; sleep 30 ; echo ; echo ; echo ; done" Enter
    sleep infinity
    sleep 2147483647
done